1. Field of the Invention
The present invention relates to a curing device which dries the paste which is used to bond chips to lead frames.
2. Prior Art
Examples of conventional curing devices are disclosed in Japanese Utility Model Application Publication (Kokoku) No. 6-19546, Japanese Patent Application Laid-Open (Kokai) Nos. 4-5838 and 5-109792, etc.
In these curing devices, a plurality of prismatic heating blocks which heat the workpieces are installed at equal intervals along the conveying direction of the workpieces. In addition, as shown in Japanese Patent Application Laid-Open (Kokai) No. 5-109792, the workpieces are successively placed on the surfaces of the heating blocks by the tact-feeding operation of a conveyor. In this conveyor, wire ropes are used. The wire ropes are installed on pulleys which are respectively installed at the workpiece entry end and workpiece exit end of the conveyor. The pulleys at one end are fastened to a drive shaft which is driven by a motor.
Accordingly, after the conveyor is raised, the wire ropes are fed by a fixed amount; and when the conveyor is lowered, the workpiece is transferred onto the surface of a heating block. The conveyor is then temporarily stopped so that the workpiece is heated. Afterward, the conveyor is raised so as to lift the workpiece from the surface of the heating block by the wire ropes. Next, the wire ropes are fed by a fixed amount, and the conveyor is then lowered so that the workpiece is conveyed onto the surface of the next heating block. As a result of this tact-feeding operation, the workpiece is successively conveyed from the workpiece entry point to the workpiece exit point.
In the prior art described above, the wire ropes are installed on pulleys which are fastened to the drive shaft, and the pulleys and wire ropes are in a state of frictional engagement. Accordingly, when the pulleys are rotated by the drive shaft so that the wire ropes are fed by a fixed amount, the wire ropes tend to slip on the drive pulleys, thereby causing the amount by which the wire ropes are fed to fluctuate. If the wire ropes are not fed by a predetermined fixed amount, the workpieces will not be placed in prescribed positions on the heating blocks, and this can lead to variation in drying quality. Furthermore, since the workpieces are conveyed by a plurality of wire ropes, variation in the amount by which the respective wire ropes are fed causes the workpieces to be positioned obliquely on the heating blocks; thus, there may be variation in the drying quality within a single workpiece.
One conceivable method of reducing slippage between the wires and the pulleys rotated by the drive shaft is to cross the wires by winding the wires around the pulleys one and a half times or more. However, with this method, it is still difficult to completely prevent wire slippage. Furthermore, if the wires are crossed, the feeding of the workpieces becomes intermittent, causing a kerchunk noise, and wire breakage tends to occur due to wire-to-wire abrasion.